This invention relates to a pharmaceutical composition and methods for treating erythropoietin disorders. More particularly, this invention is directed to methods for treating patients or animals in need of erythropoietin therapy using activin with two beta.sub.B chains.
Erythropoiesis, the production of red blood cells occurs continuously throughout the human life span to offset cell destruction. Erythropoiesis enables sufficient numbers of red blood cells to be available in the blood for proper tissue oxygenation, but not so many that the cells would impede circulation. The formation of red blood cells occurs in the bone marrow and is under the control of the hormone erythropoietin.
The amount of erythropoietin in circulating plasma increases when oxygen transport by blood cells in the circulation is reduced. This condition, called hypoxia, may be caused by large losses of blood as through hemorrhaging, radiation over-exposure that destroys red blood cells, reduction in oxygen intake due to high altitudes or prolonged unconsciousness, or various forms of anemia. Under conditions of hypoxia, erythropoietin increases the production of red blood cells by inducing the conversion of precursor cells in the bone marrow into proerythroblasts that subsequently mature, manufacture hemoglobin, and become released into the circulation as red blood cells. When the number of red blood cells in circulation is greater than needed for normal tissue oxygen requirements, the amount of erythropoietin in circulation decreases.
Many types of pharmaceuticals have been employed to relieve anemic conditions, depending on the cause. For example, iron preparations are employed generally for iron-deficiency anemia, vitamin B.sub.12 and folic acid for malignant anemia, and adrenocortical steroids, such as corticoids, for hemolytic anemia. Steroid hormones are known to have powerful erythropoietic stimulating action and are regarded as effective medicines; however, such hormones exhibit strong side effects and are generally undesirable for administration over long time periods.
Recently, erythropoietin has been proposed as an effective drug for alleviating anemia. U.S. Pat. No. 4,703,008 issued Oct. 27, 1987 describes the recombinant production of erythropoietin for producing the drug in commercially viable quantities.
Activin, which was originally identified in a study of the hormone inhibin, subsequently isolated from ovaries, and found to have follicle stimulating hormone (FSH)-releasing activity, consists of a homodimer or heterodimer of inhibin .beta. subunits, which may be .beta..sub.A or .beta..sub.B subunits. There is 95-100% amino acid conservation of .beta. subunits among human, porcine, bovine, and rat activins. The .beta..sub.A and .beta..sub.B subunits within a given species are about 64-70% homologous. The activin .beta..sub.A .beta..sub.A and .beta..sub.A .beta..sub.B dimers have been identified in follicular fluid, and the former (hereafter "Activin A") has been cloned. Mason et al., Biochem. Biophys. Res. Commun., 135: 957 (1986); EP Pub. No. 222,491 published May 20, 1987. The .beta..sub.B .beta..sub.B form of activin (hereafter "Activin B") has not been isolated thus far from a natural source, but may be produced by recombinant techniques. The complete sequence of the .beta..sub.B subunit is published in Serono Symposium Publications, entitled "Inhibin- Non-Steroidal Regulation of Follicle Stimulating Hormone Secretion", eds. H. G. Burger et al., abstract by A. J. Mason et al., vol. 42, pp 77-88 (Raven Press, 1987), entitled "Human Inhibin and Activin: Structure and Recombinant Expression in Mammalian Cells."
Activin A has been found recently to have erythropoietic-stimulating activity as well as FSH-releasing activity. See EP Publ. No. 210,461 published Feb. 4, 1987 (where the protein is called BUF-3), Eto et al., Biochem. Biophys. Res. Commun. 142: 1095-1103 (1987) and Murata et al., Proc. Natl. Acad. Sci. U.S.A., 85: 2434-2438 (1988) (where the protein is called EDF), and Yu et al., Nature, 330: 765-767 (1987) (where the protein is called FRP). In addition, Yu et al. found that the addition of Activin A significantly enhanced the formation of erythroid colony-forming units in the presence of erythropoietin up to 300%, but alone did not promote colony formation.
It is an object of the present invention to provide a method for treating erythropoietic disorders using a pharmaceutical composition encompassing Activin B.
Another object of the invention is to minimize the need for transfusion therapy, thereby reducing the chances of transmission of infectious agents.
These and other objects will become apparent to one of ordinary skill in the appropriate art.